1. Technical Field
The present disclosure relates to wireless communication apparatuses.
2. Description of Related Art
As technology advances, mobile phones are becoming increasingly popular. Although it is not clear if mobile phone electromagnetic radiation really affects human health, mobile phone users still seriously concern about the amount of mobile phone electromagnetic radiation. Even some consumers may thus change their purchase decisions.
Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed by a body tissue when exposed to a radio frequency (RF) electromagnetic field produced by a mobile phone and has units of watts per kilogram (W/kg). SAR is usually averaged over a small sample volume (typically 10 g of tissue). International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends that the SAR limit for communication apparatuses is 2 W/kg. Federal Communications Commission (FCC) recommends that the SAR limit for communication apparatuses is 1.6 W/kg.
A usual way to reduce the SAR value of a communication apparatus is to sense whether a human body is close to the antenna of the communication apparatus by a sensor disposed near the antenna of the communication apparatus. The antenna power output of the communication apparatus is reduced when the human body is close to the antenna of the communication apparatus. Such an SAR reducing method has a number of difficulties:
(1) Manufacturers have to dispose the sensing electrode of the sensor near the antenna. The sensing electrode of the sensor may affect the efficiency of the antenna because the sensing electrode of the sensor is almost always made of a conductor.
(2) The antenna efficiency of the communication apparatus is inherently lower when the human body touches the antenna of the communication apparatus. Reducing the antenna power output of the communication apparatus makes the already poor communication quality poorer.